2002 Ford Focus vehicle problem

You really haven't provided much information to go on. When does this stalling occur? Is it because the idle speed is too low? If it occurs while you're driving, the idle air control valve isn't even in the picture. Do you get a nice "idle flare-up" to 1500 rpm when you start the engine? If you do, the valve is working. If you do not, were the passages checked for being plugged with carbon when the valve was off?

When the engine stalls, what do you have to do to get it restarted?

As far as the part being needed, I can't say because I don't know if it was doing the same thing before. The fact the idle speed goes up and comes down tells me it's working and the air passages aren't blocked. 3,000 rpm is a lot. The Ford method of controlling idle speed has always had problems but to go that high suggests there may be a vacuum leak. Vacuum leaks cause an increase in engine speed without a corresponding increase in power. After you get the idle flare-up at start-up, typically to 1500 rpm, the Engine Computer wants to bring it back down to normal, and it has to close that valve more than normal to make up for the vacuum leak. Once the idle speed does come down, it will take longer for the valve to move back if engine speed drops too low. Stalling could result.

What you may need to do is have your mechanic connect a scanner to view live data so you can see what the Engine Computer is doing and what it is responding to. Problems with fuel pressure can cause stalling too, although what you described doesn't really fit with a fuel supply problem. The fuel supply system is not monitored by the Engine Computer, so there are no fault codes related to that. There ARE fault codes related to unacceptable operating conditions caused by low fuel pressure.